Method of producing group iii nitride semiconductor growth substrate

ABSTRACT

An object of the present invention is to provide a method for producing a Group III nitride semiconductor epitaxial substrate, a Group III nitride semiconductor element, and a Group III nitride semiconductor free-standing substrate, which have good crystallinity, with not only AlGaN, GaN, and GaInN the growth temperature of which is 1050° C. or less, but also with Al x Ga 1-x N having a high Al composition, the growth temperature of which is high; a Group III nitride semiconductor growth substrate used for producing these, and a method for efficiently producing those. The present invention provides a Group III nitride semiconductor growth substrate comprising a crystal growth substrate including a surface portion composed of a Group III nitride semiconductor which contains at least Al, and a scandium nitride film formed on the surface portion are provided.

This is a Division of U.S. application Ser. No. 13/259,788 filed Sep.29, 2011, which in turn is a National Phase of Application No.PCT/JP2010/055986 filed Mar. 25, 2010, which claims the benefit ofApplications JP 2009-080242 filed Mar. 27, 2009, and JP 2010-069413filed Mar. 25, 2010. Each of the disclosures of the prior applicationsis hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates to a Group III nitride semiconductorgrowth substrate, a Group III nitride semiconductor epitaxial substrate,a Group III nitride semiconductor element, and a Group III nitridesemiconductor free-standing substrate; and a method of producing thesame.

RELATED ART

For example, Group III nitride semiconductor elements including a GroupIII nitride semiconductor typically made of a chemical compound of N andsuch as Al or Ga are widely used as light emitting elements or elementsfor electronic devices. Currently, the Group III nitride semiconductoris typically formed on a crystal growth substrate made of, for example,sapphire by MOCVD.

Nevertheless, since a Group III nitride semiconductor and a crystalgrowth substrate (typically of sapphire) have very different latticeconstants, dislocation owing to the difference in the lattice constantswould arise, which causes a problem in that the crystal quality of aGroup III nitride semiconductor layer grown on a crystal growthsubstrate decreases.

To solve this problem, conventionally, a method has been widely used inwhich a GaN layer is grown on for example, a sapphire substrate with alow-temperature polycrystalline or amorphous buffer layer interposedtherebetween. However, a sapphire substrate has low thermal conductivityand can not flow electric current because of its insulating properties.Therefore, a structure is adopted in which an n-electrode and ap-electrode are formed on one surface of a sapphire substrate to flowelectric current. With such a structure, high electric current hardlyflows and little heat is dissipated, which are unsuitable formanufacturing a high power output light emitting diode (LED).

In view of this, a method such as a laser lift-off method is applied.The method uses a configuration in which such an element is transferredand attached to an additional support substrate which has sufficientelectrically conductivity and thermal conductivity, and electric currentcan flow in a vertical direction. The GaN layer formed on the sapphiresubstrate is irradiated with laser light having higher quantum energythan the energy gap of GaN to thermally decompose GaN into Ga andnitrogen, so that the Group III nitride semiconductor layer is separatedfrom the sapphire substrate.

Further, as another conventional technology, WO 2006/126330, JP2008-91728, and JP 2008-91729 disclose technique of growing a GaN layeron a sapphire substrate with a metal nitride layer interposedtherebetween. According to this method, the dislocation density of a GaNlayer can be reduced compared with the above technique, and a highquality GaN layer can be grown. This is because the differences in thelattice constants and thermal expansion coefficients between a metalnitride layer such as a CrN layer and a GaN layer are relatively small.Further, this CrN layer can be selectively etched with a chemicaletchant, which is useful in a process using a chemical lift-off method.

However, in a nitride semiconductor element for generating light of aregion of shorter wavelength than blue (for example, the wavelength of400 nm or less), as the wavelength of light to be generated is shorter,the Al component x in an Al_(x)Ga_(1-x)N layer of the nitridesemiconductor element is required to be higher. The growth temperatureof Al_(x)Ga_(1-x)N having an Al composition of more than approximately30 at. % is more than about 1050° C. that is a melting point of CrN.Therefore, when a Group III nitride semiconductor layer containingAl_(x)Ga_(1-x)N of which Al composition exceeds approximately 30 at. %is grown on a CrN layer, CrN melts under a high temperature environment,and it becomes difficult to remove CrN by chemical etching due tomaldistribution of melting CrN or the like; thus, chemical lift-off isdifficult. This shows that when a chemical lift-off method is adopted, aCrN layer can be used only when the Al composition x in theAl_(x)Ga_(1-x)N layer of the nitride semiconductor element isapproximately 0.3 or less, and the light emitting element to bemanufactured has wavelength limits. Therefore, when a chemical lift-offmethod is adopted in a device formation process, CrN can not be used asa buffer layer for growing Al_(x)Ga_(1-x)N having a high Al composition,the growth temperature of which is high. Accordingly, a material hasbeen desired which can be easily removed by chemical etching even afterheat treatment at a high temperature exceeding 1050° C. and is suitablefor a chemical lift-off method.

Although a use of a metal having a high melting point instead of CrN maybe considered, a highly corrosive hydrofluoric acid etchant isnecessarily used to remove high melting point metals (such as Zr or Hf)by dissolution due to chemical etching. When the hydrofluoric acidetchant is used in chemical lift-off, since it is so corrosive to asubstrate, an electrode, or the like that protection means are required,which is considered to lead to increase in the manufacturing costaccordingly and reduction in the degrees of freedom in a productionprocess.

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

An object of the present invention is to solve the above describedproblems by providing a Group III nitride semiconductor epitaxialsubstrate, a Group III nitride semiconductor element, and a Group IIInitride semiconductor free-standing substrate, which have goodcrystallinity, which can be used in chemical lift-off in a deviceproduction process using Al_(x)Ga_(1-x)N having a high Al composition,the growth temperature of which is high, as well as AlGaN, GaN, andGaInN, the growth temperature of which is 1050° C. or less; and a GroupIII nitride semiconductor growth substrate used for producing these.Another object of the present invention is to provide a method forefficiently producing those.

Means for Solving the Problems

To achieve the aforementioned object, the present invention primarilyincludes the following components.

(1) A Group III nitride semiconductor growth substrate comprising: acrystal growth substrate including a surface portion composed of a GroupIII nitride semiconductor which contains at least Al, and a scandiumnitride film formed on the surface portion.

(2) The Group III nitride semiconductor growth substrate according to(1) above, wherein the scandium nitride film has a crystal orientationof the {111} plane.

(3) The Group III nitride semiconductor growth substrate according to(1) or (2) above, wherein a surface of the Group III nitridesemiconductor has a crystal orientation of the {0001} plane.

(4) The Group III nitride semiconductor growth substrate according toany one of (1) to (3) above, further comprising an initial growth layercomposed of at least one layer of a buffer layer made of Al_(x)Ga_(1-x)N(0≦x≦1) on the scandium nitride film.

(5) The Group III nitride semiconductor growth substrate according toany one of (1) to (4) above, wherein a thickness of the scandium nitridefilm is 3 nm to 100 nm.

(6) The Group III nitride semiconductor growth substrate according toany one of (1) to (5) above, wherein a base substrate of the crystalgrowth substrate is selected from the group consisting of sapphire, Si,SiC, and GaN.

(7) The Group III nitride semiconductor growth substrate according toany one of (1) to (6) above, wherein the surface portion is made of AlN.

(8) The Group III nitride semiconductor growth substrate according toany one of (1) to (7) above, wherein the scandium nitride film has aplurality of microcrystal portions having a triangular pyramid shape,and the plurality of microcrystal portions are uniformly formed on thesurface portion.

(9) A Group III nitride semiconductor epitaxial substrate comprising atleast one layer of a Group III nitride semiconductor layer on the GroupIII nitride semiconductor growth substrate according to any one of (1)to (8) above.

(10) A Group III nitride semiconductor free-standing substrate producedusing the Group III nitride semiconductor growth substrate according toany one of (1) to (8) above.

(11) A Group III nitride semiconductor element produced using the GroupIII nitride semiconductor growth substrate according to any one of (1)to (8) above.

(12) A method of producing a Group III nitride semiconductor growthsubstrate, comprising: a step of forming a metal layer made of a Scmaterial on a crystal growth substrate including a surface portioncomposed of a Group III nitride semiconductor which contains at leastAl, and a step of performing a nitriding process by heating the metallayer in an ambient gas containing an ammonia gas, thereby forming ascandium nitride film.

(13) The method of producing a Group III nitride semiconductor growthsubstrate, according to (12) above, wherein the ambient gas containingthe ammonia gas is a mixed gas further containing one or more selectedfrom an inert gas and a hydrogen gas.

(14) The method of producing a Group III nitride semiconductor growthsubstrate, according to (12) or (13) above, wherein a highesttemperature for heating the metal layer is in the range of 850° C. to1300° C., and heating time at 850° C. or higher is 1 min to 120 min.

(15) The method of producing a Group III nitride semiconductor growthsubstrate, according to any one of (12) to (14) above, furthercomprising a step of forming an initial growth layer composed of atleast one layer of a buffer layer made of Al_(x)Ga_(1-x)N (0≦x≦1) on thescandium nitride film after the step of the nitriding process.

(16) A method of producing a Group III nitride semiconductor element,comprising: a step of forming a metal layer made of a Sc material on acrystal growth substrate including a surface portion composed of a GroupIII nitride semiconductor which contains at least Al; a step ofperforming a nitriding process by heating the metal layer in an ambientgas containing an ammonia gas to form a scandium nitride film, therebyproducing a Group III nitride semiconductor growth substrate; a step ofepitaxially growing at least one layer of a Group III nitridesemiconductor layer over the Group III nitride semiconductor growthsubstrate, thereby producing a Group III nitride semiconductor epitaxialsubstrate; a step of isolating the Group III nitride semiconductor layerinto a plurality of elements; a step of forming a support substrate onthe Group III nitride semiconductor layer side; and a step of separatingthe Group III nitride semiconductor layer from the crystal growthsubstrate by chemical lift-off by selectively etching the scandiumnitride film, thereby obtaining a Group III nitride semiconductorelement.

(17) The method of producing a Group III nitride semiconductor element,according to (16) above, wherein the Group III nitride semiconductorlayer is grown at a highest temperature in the range of 900° C. to 1300°C. in the step of producing the Group III nitride semiconductorepitaxial substrate.

(18) The method of producing a Group III nitride semiconductor element,according to (16) or (17) above, further comprising a step of forming aninitial growth layer composed of at least one layer of a buffer layermade of Al_(x)Ga_(1-x)N (0≦x≦1) on the scandium nitride film afterperforming the nitriding process.

(19) The method of producing a Group III nitride semiconductor element,according to (18) above, wherein the initial growth layer is composed ofa first buffer layer and a second buffer layer grown on the first bufferlayer, a growth temperature of the first buffer layer is in the range of900° C. to 1260° C., a growth temperature of the second buffer layer isin the range of 1030° C. to 1300° C., and the growth temperature of thefirst buffer layer is equal to or lower than the growth temperature ofthe second buffer layer.

(20) A method of producing a Group III nitride semiconductorfree-standing substrate, comprising: a step of forming a metal layermade of a Sc material on a crystal growth substrate including a surfaceportion composed of a Group III nitride semiconductor which contains atleast Al; a step of performing a nitriding process by heating the metallayer in an ambient gas containing an ammonia gas to form a scandiumnitride film, thereby producing a Group III nitride semiconductor growthsubstrate; a step of epitaxially growing at least one layer of a GroupIII nitride semiconductor layer over the Group III nitride semiconductorgrowth substrate; and a step of separating the Group III nitridesemiconductor layer from the crystal growth substrate by chemicallift-off by selectively etching the scandium nitride film, therebyobtaining a Group III nitride semiconductor free-standing substrate.

(21) The method of producing a Group III nitride semiconductorfree-standing substrate, according to (20) above, wherein the Group IIInitride semiconductor layer is grown at a highest temperature in therange of 900° C. to 1300° C. in the step for producing the Group IIInitride semiconductor epitaxial substrate.

Effect of the Invention

A Group III nitride semiconductor growth substrate of the presentinvention comprises a crystal growth substrate including a surfaceportion composed of a Group III nitride semiconductor which contains atleast Al, and a scandium nitride film formed on the surface portion.Thus, without greatly reducing the crystallinity of a Group III nitridesemiconductor layer Al_(x)Ga_(y)In_(1-x-y)N (0≦x≦1, 0≦x+y≦1) to beformed later, the Group III nitride semiconductor layer can be easilyseparated from the crystal growth substrate by chemical lift-off.

Further, in chemical lift-off, an acid solution is used as an etchant,which allows the Group III nitride semiconductor layer to be easilyseparated from the crystal growth substrate. As the etchant, ahydrochloric acid aqueous solution, a nitric acid aqueous solution, amixed acid of sulfuric acid and nitric acid, organic acid, or the likecan be used, and an acid solution which dissolves only ScN withoutdissolving the materials of the support substrate or the electrode to beused is appropriately selected.

Furthermore, according to the present invention, the above Group IIInitride semiconductor growth substrate is used, which allows thesubstrate to be removed by chemical lift-off. Besides, a Group IIInitride semiconductor epitaxial substrate, a Group III nitridesemiconductor element, and a Group III nitride semiconductorfree-standing substrate, which have good crystallinity can be provided,which can cover all wavelengths (200 nm to 1.5 μm) covered by a GroupIII nitride semiconductor material which exceeds the wavelength limit ofthe case of using a CrN material, in other words, which can cover thegrowth temperature range of the whole composition range ofAl_(x)Ga_(y)In_(1-x-y)N (0≦x≦1, 0≦y≦1, 0≦x+y≦1) including from MN grownat a high temperature of 1200° C. or more to InN grown at a temperatureof about 500° C.

Moreover, according to the present invention, a step of forming a metallayer made of a Sc material on a crystal growth substrate a surfaceportion composed of a Group III nitride semiconductor which contains atleast Al, and a step of performing a nitriding process to the metallayer are provided. Thus, a Group III nitride semiconductor growthsubstrate can be produced such that the Group III nitride semiconductorlayer can be easily separated from the crystal growth substrate bychemical lift-off without greatly reducing the crystallinity of theGroup III nitride semiconductor layer Al_(x)Ga_(y)In_(1-x-y)N (0≦x≦1,0≦y≦1, 0≦x+y≦1) to be formed later.

In addition, in accordance with the present invention, chemical lift-offis performed using the above Group III nitride semiconductor growthsubstrate. Thus, a Group III nitride semiconductor epitaxial substrate,a Group III nitride semiconductor element, and a Group III nitridesemiconductor free-standing substrate, which have good crystallinity canbe produced efficiently, which can cover all wavelengths (200 nm to 1.5μm) covered by a Group III nitride semiconductor material which exceedsthe wavelength limit of the case of using a CrN material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating a cross-sectional configurationof a nitride semiconductor growth substrate according to the presentinvention;

FIG. 2 is a schematic view illustrating a production process of anitride semiconductor element according to the present invention;

FIG. 3 is a graph illustrating a result of 2θ/ω scan measurement usingan x-ray diffractometer;

FIG. 4 is a SEM image of a surface of a sample according to the presentinvention;

FIG. 5 is a SEM image of a surface of a sample according to the presentinvention;

FIG. 6 is a SEM image of a surface of a sample according to the presentinvention;

FIG. 7 is a SEM image of a surface of a sample according to the presentinvention;

FIG. 8 is an surface height image of a sample according to the presentinvention obtained using an AFM (atomic force microscope); and

FIG. 9 is a graph illustrating light emission spectrum of a sampleaccording to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, an embodiment of a Group III nitride semiconductor growthsubstrate of the present invention will be described with reference tothe drawings. Here, a Group III nitride semiconductor epitaxialsubstrate in the present invention refers to a substrate in which atleast one layer of a Group III nitride semiconductor layer is grown onthe Group III nitride semiconductor growth substrate. A Group IIInitride semiconductor element refers to an element obtained byperforming a device process such as vapor deposition for forming anelectrode to the above Group III nitride semiconductor epitaxialsubstrate and an element isolated from the above Group III nitridesemiconductor epitaxial substrate. Further, a Group III nitridesemiconductor free-standing substrate refers to a substrate obtained bygrowing a Group III nitride semiconductor layer having a thickness of atleast 50 μM or more on the above Group III nitride semiconductor growthsubstrate and then separating the Group III nitride semiconductor growthsubstrate. FIG. 1 schematically illustrates a cross-sectionalconfiguration of a Group III nitride semiconductor growth substrate inaccordance with this invention.

A Group III nitride semiconductor growth substrate 1 shown in FIG. 1comprises a crystal growth substrate 3 including at least a surfaceportion 2 composed of a Group III nitride semiconductor which containsat least Al, and a nitride film 4 made of scandium nitride formed on thesurface portion 2. With such a structure, without greatly reducing thecrystallinity of a Group III nitride semiconductor layer to be formedover the scandium nitride film 4 later, the crystal growth substrate 3can be separated from the Group III nitride semiconductor layer bychemical lift-off. Note that hatching in the figure is added for thesake of explanation.

The Group III nitride semiconductor growth substrate 1 preferablyfurther includes an initial growth layer composed of at least one layermade of Al_(x)Ga_(1-x)N (0≦x≦1), especially in FIG. 1, an initial growthlayer 5 composed of two layers of buffer layers 5 a and 5 b formed onthe scandium nitride film 4. This improves the crystallinity of thenitride semiconductors layer to be grown thereon. The Al composition inthese buffer layers can be selected as appropriate depending on thematerial to be formed thereon. Note that these buffer layers may containa small amount of In.

The crystal growth substrate 3 may be a template substrate having theGroup III nitride semiconductors 2 containing at least Al on a basesubstrate 6 made of a material used for growing a Group III nitridesemiconductor such as sapphire, Si, SiC, GaN or AlGaN. Alternatively,the crystal growth substrate 3 may be a single crystal substrate of theGroup III nitride semiconductors 2 or a surface nitrided sapphiresubstrate formed by nitriding a surface of sapphire. FIG. 1 illustratesthe case where the crystal growth substrate 3 is an AlN templatesubstrate having an AlN single crystal layer 2 on a sapphire substrate6. This surface portion 2 made of Group III nitride semiconductorcontaining at least Al has an effect of reducing crystal defects in anAlGaN layer to be grown thereon.

At least the surface portion 2 of the crystal growth substrate 3 ispreferably made of Al_(x)Ga_(1-x)N (0.5≦x≦1) having an Al composition of50 at. % or more, more preferably of Al_(x)Ga_(1-x)N (0.8≦x≦1) having anAl composition of 80 at. % or more. When the Al composition of thecrystal growth substrate 3 is as much as that of the Group III nitridesemiconductor layer to be grown thereover, homoepitaxial growth occurs.This allows growth of a layer having good crystallinity with a lowdislocation defect density. In addition, the surface portion 2 is mostpreferably made of AlN since when the Al composition of the crystalgrowth substrate 3 is higher than that of the Group III nitridesemiconductor layer to be grown thereover, further effect of reducingdislocation can be expected because of compressive stress, and since thegrowth temperature of AlN is highest among the Group III nitridesemiconductor materials, and besides it dose not deteriorate when theGroup III nitride semiconductor layer is formed thereon.

The scandium nitride (ScN) film 4 can be obtained by nitriding a Scmetal film. A ScN material has excellent properties of having a highmelting point and being able to be removed by dissolution using variouskinds of acid solutions as an etchant. Further, a ScN crystal have ahalite structure; however, when at least the surface portion 2 of thecrystal growth substrate 3 is a Group III nitride semiconductor materialcontaining Al, the ScN crystal is oriented to have the (111) plane witha 3-fold rotation axis which is the same as the crystal structure of theGroup III nitride semiconductor containing Al, and the lattice constantand the coefficient of linear expansion along the a-axis of ScNapproximate to those of the Group III nitride semiconductor containingAl. Unlike the case of using CrN, when ScN is directly formed on asapphire substrate without the Group III nitride semiconductor materialcontaining Al therebetween, the orientation degree of ScN decreases onaccount of the great difference in lattice constants between ScN andsapphire. Therefore, it is difficult to grow a high quality Group IIInitride semiconductor layer thereon.

The scandium nitride film 4 preferably has a thickness of 3 nm to 100nm. When the thickness is less than 3 nm, the scandium nitride film 4 isso thin that an etchant would be less likely to infiltrate, or thethickness of the metal Sc layer would be discontinuous due to nitriding,which would expose a surface of the crystal growth substrate as a groundsubstrate, so that the Group III nitride semiconductor layer would bedirectly grown on the crystal growth substrate. Such circumstances wouldmake it difficult to perform chemical lift-off. On the other hand, whenthe thickness exceeds 100 nm, increase in the crystallinity due to thesolid-state epitaxy of the scandium nitride film itself cannot beexpected, which would reduce the crystallinity of the Group III nitridesemiconductor layer thereon, and defects might increase. Further, thisscandium nitride film 4 can be formed by forming a metal Sc layer on thecrystal growth substrate 3 by a method such as sputtering or vacuumvapor deposition and then nitriding the metal Sc layer.

Although not shown in FIG. 1, at least one layer of a Group III nitridesemiconductor layer is provided on the Group III nitride semiconductorgrowth substrate 1 having the above-described structure; thus, a GroupIII nitride semiconductor epitaxial substrate in accordance with thepresent invention can be obtained.

Similarly, although not shown in FIG. 1, using the Group III nitridesemiconductor growth substrate 1 having the above-described structure, aGroup III nitride semiconductor free-standing substrate and a Group IIInitride semiconductor element in accordance with the present inventioncan be obtained.

Next, an embodiment of a method of producing a Group III nitridesemiconductor growth substrate of the present invention will bedescribed with reference to the drawings.

The method of producing the Group III nitride semiconductor growthsubstrate 1 of the present invention can be produced by, as shown inFIG. 1, a step of forming a single metal layer made of a Sc material onthe crystal growth substrate 3 including the surface portion 2 composedof the Group III nitride semiconductor which contains at least Al, and astep of nitriding the metal layer to form the scandium nitride film 4.With such a structure, without greatly reducing the crystallinity of theGroup III nitride semiconductor layer to be formed thereover, thecrystal growth substrate 3 can be separated from the Group III nitridesemiconductor layer by chemical lift-off.

For example, sapphire, Si, SiC, GaN, AlGaN, AlN, or the like can be usedfor the base substrate 6. In terms of cost of procuring a substrate,sapphire or Si can be preferably used in particular. The metal layermade of a Sc material can be formed by sputtering. Although vapordeposition is possible, sputtering is preferable.

The nitriding of the Sc material can be performed by heating in a mixedgas containing ammonia, and further containing one or two of an inertgas (one or more selected from rare gases such as N₂, Ar, He, and Ne)and a hydrogen gas; or in an ammonia gas. Since the Sc material issublimable, it is preferable to start flowing the synthetic gas orammonia gas at a temperature lower than the sublimation temperature inthe elevated temperature process. Thus, Sc is nitrided to form ScN,which is a material stable under high temperatures. Alternatively, it ispermissible to start to flow the synthetic gas or ammonia gas at roomtemperature; however, it is preferable to start to flow the syntheticgas or ammonia gas at a temperature in the vicinity of 500° C., thedecomposition temperature of ammonia, since wasting of the ammonia gascan be prevented, which leads to cost reduction. A highest temperatureof the heating temperature (temperature of the surface of basesubstrate) is preferably 850° C. to 1300° C. When it is lower than 850°C., nitriding cannot be conducted sufficiently in some cases. When it ishigher than 1300° C., the high temperature would shorten the equipmentlife. The heating is performed so that the time where 850° C. or higheris kept is preferably in the range of 1 minute to 120 minutes. When thetime is shorter than 1 minute, nitriding may not be performedsufficiently. When the time is longer than 120 minute, it is notparticularly effective and is disadvantageous in terms of productivity.The kind of inert gas is not limited in particular, and N, Ar, or thelike can be used. A concentration of the ammonia gas is preferably inthe range of 0.01 vol % to 100 vol %. When the concentration is lessthan the lower limit, nitriding may not be performed sufficiently. Whenthe ammonia gas concentration is too high, the surface roughness afterthe nitriding process may be high. Therefore, the concentration of theammonia gas is more preferably 0.01 vol % to 90 vol %. Further, themixed gas may contain hydrogen at 20 vol % or less.

Note that even under the conditions where the nitriding may beinsufficient, as long as at least the surface of the Sc material wouldfind becoming ScN which is oriented to have the (111) plane, a Group IIInitride semiconductors can be grown.

A step of forming the initial growth layer 5 composed of at least onelayer of a buffer layer made of an Al_(x)Ga_(1-x)N material (0≦x≦1) onthe scandium nitride film 4 is preferably added. This is for improvingthe crystallinity of the Group III nitride semiconductor layer to beformed later, and its growth temperature is preferably in the range of900° C. to 1300° C. Note that the initial growth layer may be formed bya known growth method such as MOCVD, HYPE (hydride vapor phase epitaxy),PLD (pulsed laser deposition).

The Group III nitride semiconductor growth substrate 1 in accordancewith the present invention can be produced using the above-describedmethods.

Next, as shown in FIG. 2A, a method of producing a Group III nitridesemiconductor epitaxial substrate 8 according to the present inventionincludes a step of epitaxially growing at least one layer of a Group IIInitride semiconductor layer 7 over the Group III nitride semiconductorgrowth substrate 1 manufactured by the above method. With such astructure, the Group III nitride semiconductor epitaxial substratehaving good crystallinity can be produced which can cover the growthtemperature range of the whole composition range of the Group IIInitride semiconductor material, which exceeds the temperature limit(wavelength limit) of the case of using a CrN material for removing thecrystal growth substrate 3 to be described later by chemical lift-off.

The Group III nitride semiconductor layer 7 is preferably grown at thehighest temperature range of 900° C. to 1300° C. by MOCVD, HVPE, PLD,MBE, or the like.

It is preferable to additionally form the initial growth layer 5composed of at least one layer of a buffer layer made of anAl_(x)Ga_(1-x)N material (0≦x≦1) on the scandium nitride film 4. This isfor improving the crystallinity of the Group III nitride semiconductorlayer 7 to be formed later, and its growth temperature is preferably inthe range of 900° C. to 1300° C.

The initial growth layer 5 may be composed of a single layer; however,preferably composed of two or more layers in terms of improving thecrystallinity of the Group III nitride semiconductor layer 7 formedlater. When the initial growth layer 5 has two layers, it is preferablethat the initial growth layer 5 has a first buffer layer 5 a and asecond buffer layer 5 b grown on the first buffer layer 5 a; a growthtemperature of the first buffer layer 5 a is in the range of 900° C. to1260° C.; a growth temperature of the second buffer layer 5 b is in therange of 1000° C. to 1300° C.; and the growth temperature of the firstbuffer layer 5 a is lower than that of the second buffer layer 5 b. Inan initial growth stage of growing the first buffer layer 5 a, thegrowth is performed at a relatively low temperature so that many initialgrowth nuclei are promoted to be formed to improve the crystallinity,and the second buffer layer 5 b to be grown later is grown at a hightemperature. Thus, grooves and cavities formed between many initialnuclei are filled, so that the flatness can be improved as well as theimprovement in the crystallinity. Further, the buffer layer may havethree or more layers. In that case, the growth temperatures arepreferably higher in order. When the initial growth layer 5 has onelayer, the growth temperature is preferably in the range of 1000° C. to1300° C.

The Group III nitride semiconductor epitaxial substrate 8 in accordancewith the present invention can be manufactured using the above describedmethod.

Next, as shown in FIG. 2A and FIG. 2B, a method of producing a Group IIInitride semiconductor element 9 of the present invention is performed onthe Group III nitride semiconductor epitaxial substrate 8 formed by theabove method. The method includes a step of isolating the Group IIInitride semiconductor layer 7 having at least one layer into a pluralityof elements, a step of forming a support substrate 10 on the Group IIInitride semiconductor layer 7 side, and a step of selectively etchingthe scandium nitride film 4 to separate the Group III nitridesemiconductor layer 7 (in the case of FIG. 2B, the Group III nitridesemiconductor layer 7 and the buffer layer 5) from the crystal growthsubstrate 3 by chemical lift-off, so that the Group III nitridesemiconductor element 9 is obtained. With such a structure, the GroupIII nitride semiconductor element having good crystallinity can beefficiently produced, which can cover the growth temperature range ofthe whole composition range of the Group III nitride semiconductormaterial, which exceeds the temperature limit (wavelength limit) of thecase of using a CrN material for removing the crystal growth substrate 3by chemical lift-off.

The Group III nitride semiconductor layer 7 having at least one layermay be composed of for example, an n-AlGaN layer 11, an AlInGaN-basedquantum well active layer 12, and a p-AlGaN layer 13 as shown in FIG. 2Aand FIG. 2B. Note that the conductivity types of these Group III nitridesemiconductor layers 11, 12, and 13 may be in the opposite order.Further, the support substrate 10 is preferably formed of a heatdissipating material.

The Group III nitride semiconductor element 9 in accordance with thepresent invention can be produced by the above method.

Next, a method of producing a Group III nitride semiconductorfree-standing substrate of the present invention includes a step ofepitaxially growing a Group III nitride semiconductor layer having atleast one layer over the Group III nitride semiconductor growthsubstrate manufactured by the above described method, and a step ofselectively etching the scandium nitride film 4 to separate the GroupIII nitride semiconductor layer from the crystal growth substrate bychemical lift-off thereby obtaining the Group III nitride semiconductorfree-standing substrate. With such a structure, the Group III nitridesemiconductor free-standing substrate having good crystallinity can beefficiently produced, which can cover the growth temperature range ofthe whole composition range of the Group III nitride semiconductormaterial, which exceeds the temperature limit (wavelength limit) of thecase of using a CrN material for removing the crystal growth substrate 3by chemical lift-off.

A thickness of the Group III nitride semiconductor layer may be 50 μm ormore. This ensures easy handling.

The Group III nitride semiconductor free-standing substrate inaccordance with the present invention can be produced using the abovemethod.

Note that the above description was made to show examples ofrepresentative embodiments, and the present invention is not limited tothose embodiments.

EXAMPLE Example 1

An AlN single crystal layer (thickness: 1 μm) was grown on sapphireusing MOCVD to manufacture an AlN (0001) template substrate as a nitridesemiconductor growth substrate. On the obtained AlN template substrate,Sc was deposited to a thickness shown in Table 1 by sputtering, and thenthe substrate was set in an MOCVD apparatus. A mixed gas of a nitrogengas and an ammonia gas was flown at a flow rate in Table 1; heating wasperformed to a temperature (substrate surface temperature) in Table 1under that atmosphere; and the temperature was kept at a pressure of 200Torr for 10 minutes. Thus, a nitriding process was performed. Afterthat, cooling was performed for 70 min to room temperature, and thesubstrate was taken out of the MOCVD apparatus; thus, five kinds ofsamples of 1-1 to 1-5 were obtained.

TABLE 1 atmosphere, flow rate Metal layer nitriding process whole flowx-ray diffraction Sample metal thickness temperature pressure time NH₃N₂ rate peak No. species (nm) (deg. C.) (Torr) (min) (%) (%) (SLM)ScN(111) 1-1 Sc 10 1200 200 10 30 70 3.5 observed Example 1-2 10 1100200 10 30 70 3.5 observed Example 1-3 10 1000 200 10 30 70 3.5 observedExample 1-4 20 1200 200 10 30 70 3.5 observed Example 1-5 20 830 200 1030 70 3.5 not observed Comparative Example

(Evaluation)

2θ/ω scan measurement was performed on each of the five samples using anx-ray diffractometer to evaluate the crystallization and crystalorientation of the scandium nitride film. FIG. 3 shows the measurementresults. The horizontal axis represents the angle of 20 while thevertical axis represents the intensity of a diffraction x-ray. Withrespect to Samples 1-1 to 1-4, in addition to diffraction peaks ofsapphire and AlN derived from the AlN template used as a groundsubstrate, diffraction peaks of (111) and (222) of ScN were observed.This result shows that the Sc film was nitrided to form ScN having acrystal orientation of the (111) plane.

With respect to Sample 1-5 subjected to a nitriding process at a lowtemperature of 830° C., x-ray diffraction peaks of (111) and (222) ofScN were not observed, and ScN of (111) orientation was not formed.

Further, FIG. 4 to FIG. 7 show results of observing the surface of eachof the samples 1-1 to 1-4 magnified 100,000 times with a scanningelectron microscope (SEM). In FIG. 4 in particular, a plurality ofprotrusions having a triangular pyramid shape existed on the surface ofthe scandium nitride film, and each of the protrusions was theapproximately same in size, and the protrusions were tightly arranged.Such protrusions were distributed uniformly on the entire surface of theground substrate. The triangular pyramids had two kinds of directions oftheir bases, and the directions of the bases were along <1-100>directions of the AlN (0001) of the surface of the ground substrate.Further, the surfaces other than the bottom surfaces of the triangularpyramids are composed of approximate {100} planes.

When Samples 1-1 to 1-4 were immersed in etchants below at roomtemperature, the ScN film of each of the four kinds of samples wasobserved to be removed by each of the etchants.

Note <Etchants>

hydrofluoric acid (46%), buffered hydrofluoric acid (NH₄HF₂: 17.1%,NHF₄: 18.9%), nitric acid (61%), hydrochloric acid (36%), sulfuric acid(96%), mixed acid of sulfuric acid and nitric acid (the sulfuric acid:the nitric acid=9:1), malic acid, citric acid, acidum tartaricum (%means mass %)

As described above, a ScN film of the present invention can be removedusing a wide variety of acid solutions and can be selected depending ona support substrate, a electrode, and a bonding material.

Example 2

As is the case with Example 1, a single metal layer of the metal speciesand thickness shown in Table 2 was formed on an AlN (0001) templatesubstrate by sputtering. Thus formed samples were treated by a nitridingprocess under the conditions of Table 2 as in Example 1. Note thatSample 2-2 is a comparative example which was not nitrided, and wastreated by heat treatment in a hydrogen gas. Following after that, abuffer layer made of an AlN material (1 μm) was further formed by MOCVDunder the conditions shown in Table 2 to obtain Samples 2-1 to 2-3. Thesource gas of Al was TMA.

TABLE 2 atmosphere, flow rate Metal layer process conditions wholebuffer layer Sample metal thickness temperature pressure time NH₃ N₂ H₂flow rate temperature pressure V/III No. species (nm) (deg. C.) (Torr)(min) (%) (%) (%) (SLM) (deg. C.) (Torr) ratio 2-1 Sc 10 1200 200 10 3070 — 3.5 1125 10 120 Example 2-2 20 1200 200 10 — — 100 3.5 1125 12 120Comparative Example 2-3 Cr 20 1200 200 10 10 20 70 3.5 1125 12 120Comparative Example

(Evaluation)

An x-ray rocking curve measurement was performed on the (0002) plane andthe (10-12) plane of AlN of the AlN buffer layers of Samples 2-1 to 2-3,and surface evenness of the AlN buffer layers of Samples 2-1 to 2-3 wasevaluated using an AFM. The results are shown in Table 3. The full widthat half maximum of an x-ray rocking curve of Sample 2-1 in which themetal nitride layer was made of ScN was nearly equivalent to that ofSample 2-3 in which the metal nitride layer was made of CrN as shown inTable 3. Further, the crystallinity of the AlN buffer layer of Sample2-1 was approximately equivalent to that of Sample 2-3, and wasfavorable.

A 850 μm □ (square) SiO₂ pattern was formed as a mask in each of Samples2-1 to 2-3, and the AlN buffer layer was etched by dry etching to form agroove portion in which the metal nitride layer was exposed. After that,a bonding layer containing Au was formed on the AlN buffer layer and wasbonded to a support substrate. A material of the support substrate wasselected, which is tolerant to an aqueous solution used in etching. Thecombinations of the support substrate and the etchant are as shown inConditions 1 to 4 below.

Note

Condition 1 aqueous solution containing hydrofluoric acid: HF (46 mass%)

(support substrate: Mo, bonding layer: Au—Sn)

Condition 2 aqueous solution containing nitric acid: HNO₃ (61 mass %)

(support substrate: Si, bonding layer: Au—Au)

Condition 3 aqueous solution containing hydrochloric acid: HCl (36 mass%)

(support substrate: Si, bonding layer: Au—Au)

Condition 4 aqueous solution containing Cr etchant: (NH₄)₂Ce(NO₃)₆ (14mass %) and HNO₃ (3 mass %)

(support substrate: Si, bonding layer: Au—Au)

Under these Conditions 1 to 4, the temperature of each of the aqueoussolutions was set at 25° C., and Samples 2-1 to 2-3 were immersed for 24hours.

Table 4 shows the results. In Table 4, a circle mark (o) represents thecase when the AlN buffer layer and the growth substrate was separated,and a cross mark (x) represents the case when they could not beseparated. In Sample 2-1, lift-off is possible under all the conditions.In Sample 2-2, sublimation of metallic Sc eliminated the metal layerwhich was a layer to be etched, and the AlN buffer layer was formeddirectly on the AlN template. Therefore, lift-off is considered to havebeen impossible. In Sample 2-3, CrN melted under a high temperature, andwas rendered unable to cover the entire surface, so that the AlN bufferlayer was partially formed directly on the AlN template. Therefore,lift-off is considered to have been impossible.

TABLE 3 XRC for AlN AFM Sample (0002) (10-12) Ra No. metal species[arcsec] [arcsec] [Å] 2-1 Sc 85 1611 165 Example 2-2 75 1420 2.3Comparative Example 2-3 Cr 52 1505 2.0 Comparative Example

TABLE 4 Sample No. Condition 1 Condition 2 Condition 3 Condition 4 2-1 ∘∘ ∘ ∘ 2-2 x x x x 2-3 x x x x

Example 3

As is the case with Example 1, a Sc metal layer was formed to athickness shown in Table 5 on an AlN (0001) template substrate bysputtering, and thereafter a nitriding process was performed under theconditions shown in Table 5. With respect to thus formed samples, one ortwo layers of buffer layers made of an AlN material were formed underthe conditions shown in Table 5 to obtain Samples 3-1 and 3-2. Note thatfilm formation conditions other than the conditions shown in Table 5were the same as those in the case of Example 2.

TABLE 5 buffer layers second buffer layer nitriding process first bufferlayer heating Sample metal thickness temperature pressure timetemperature pressure time time temperature time No. species (nm) (deg.C.) (Torr) (min) (deg. C) (Torr) (min) (min) (deg. C.) (min) 3-1 Sc 101200 200 10 1040 10 1 5 1170 49 Example 3-2 10 1200 200 10 1170 10 50Example

(Evaluation)

FIG. 8 shows a sample surface image of Sample 3-1, obtained by AFM.Atomic steps was observed, which shows that an AlN layer which was flatat the atomic level was obtained. On the other hand, with respect toSample 3-2, great unevenness was caused by surface roughness andmeasurement with the AFM was difficult.

The result of evaluating an x-ray rocking curve of the AlN buffer layerin Samples 3-1 and 3-2 with the same method as the cases of Samples 2-1to 2-3, and the results of measuring Ra of the AlN buffer layer with theAFM are shown in Table 6. In Sample 3-1, in which the AlN buffer layerhad two layers on the metal layer, Ra was greatly improved compared withSample 3-2, in which the AlN buffer layer had one layer. If the AlNbuffer layer has two layers, the surface evenness of the AlN bufferlayer can be improved.

TABLE 6 XRC for AlN AFM Sample metal (0002) (10-12) Ra No. species[arcsec] [arcsec] [Å] 3-1 Sc 109 1649 2.2 Example 3-2 181 1454

Example

Example 4

As is the case with Example 1, a 15 nm-thick Sc metal layer was formedon an AlN (0001) template substrate having a diameter of two inches bysputtering, and thereafter a nitriding process was performed in an MOCVDapparatus at a pressure of 200 Torr and a substrate temperature of 1150°C. for 10 minutes. Here, the mixing ratio between NH₃ and N₂ was 30:70each in volume percentage.

After the nitriding process, the substrate temperature was lowered to1020° C., and AlN as a first buffer layer was grown to 80 nm on thescandium nitride film under the condition of a pressure of 10 Torr.After that, the substrate temperature was raised to 1200° C. and an AlNlayer was grown to 920 nm as a second buffer layer. The ratio of V/IIIat the time of AlN growth was 120, and the growth rate was about 1000nm/hr.

Subsequently, a 2.5 μm thick n-type AlGaN cladding layer, a MQW(multiple quantum well) light emitting layer of AlInGaN/AlGaN, a p-typeAlGaN electron blocking layer, a p-type AlGaN cladding layer, and ap-type AlGaN contact layer (total thickness of the p-type layers was 25μm) were grown in an MOCVD furnace to obtain an epitaxial substratehaving an UV-LED structure.

Epitaxial layers of this epitaxial substrate were grooved with a gridpattern by dry etching to the AlN template portion to perform primaryisolation into individual LED chips. Next, a Rh-based ohmic electrodewas formed on the p-type contact layer and then bonded with a lowresistivity p-type silicon substrate by vacuum hot press with anAuSu-based bonding layer interposed therebetween. The scandium nitridefilm was selectively dissolved using hydrochloric acid by using thegrooved portion as an etching channel, and consequently, the epitaxialportion having the LED structure was separated from the growth substrateand transferred to the Si support substrate side. Note that an ohmicelectrode to be a positive electrode was formed on the backside of theSi substrate.

At least a part of the AlN layer was removed by dry etching and aTi/Al-based ohmic electrode was formed on the part of the n-type AlGaNcladding layer exposed by etching. Dicing was performed along theprimary isolation groove with a blade dicer to obtain individual piecesof LED chips. Characteristic of the obtained UV LED having a verticalstructure was evaluated and the LED exhibited an emission spectrum witha peak wavelength of 326 nm as shown in FIG. 9. Further, light poweroutput was 2.5 mW with a forward drive current I_(f) of 20 mA, which wasa very favorable result for this wavelength range. Note that when Cr wasused as a metal layer on the AlN template substrate, the substrateexperienced a temperature of 1200° C. before epitaxial growth for theUV-LED structure, and the subsequent process steps could not beperformed, and LEDs of such a wavelength was not obtained.

Example 5

As is the case with Example 1, a 15 nm-thick Sc metal layer was formedon an AlN (0001) template substrate having a diameter of two inches bysputtering, and thereafter a nitriding process was performed in an MOCVDapparatus at a pressure of 200 Torr and a substrate temperature of 1150°C. for 10 minutes. Here, the mixing ratio between NH₃ and N₂ was 30:70each in volume percentage.

After the nitriding process, the substrate temperature was lowered to1020° C., and AlN as a first buffer layer was grown to 80 nm on thescandium nitride film under the condition of a pressure of 10 Torr.After that, the substrate temperature was raised to 1200° C. and an AlNlayer was grown to 920 nm as a second buffer layer. The ratio of V/IIIat the time of AlN growth was 120, and the growth rate was about 1000nm/hr. The source gas of Al was TMA.

After then raising the substrate temperature to 1250° C., the feed rateof TMA was doubled while keeping the V/III ratio to grow an AlN layerwith a thickness of 100 μm for 48 hours. After cooling and taking out,the substrate was immersed in hydrochloric acid to selectively etch thescandium nitride film and separate the AlN template substrate for growthto obtain, an AlN single crystal free-standing substrate having adiameter of two inches.

Example 6

As is the case with Example 1, a 20 nm-thick Sc metal layer was formedon an AlN (0001) template substrate having a diameter of two inches bysputtering, and then a nitriding process was performed in an MOCVDapparatus at a pressure of 200 Torr and a substrate temperature of 1200°C. for 10 minutes.

After the nitriding process, the substrate temperature was lowered to900° C. to perform initial growth of a GaN layer for 10 minutes, andthen thick film growth (thickness of approximately 7 μm) of GaN wasperformed at a substrate temperature of 1040° C. for two hours. Aftercooling and taking out, the sample was set in an HVPE furnace and thesubstrate temperature was raised to 1040° C. at a heating rate of 20°C/min. Note that concurrently with the heating of the substrate, thetemperature of Ga material source portion was heated to 850° C. Notefurther that the flow rate of the ambient gas was as follows: N₂-300sccm, H₂-100 sccm, and NH₃-1000 sccm from the point of 600° C. duringthe rise in temperature of the samples. The substrate temperature waskept at 1040° C. for about five minutes for the system temperature beingstable, and supply of HCl to the Ga source portion was started at a flowrate of 40 sccm to start to grow GaN. Two hours later, the supply of HClwas stopped to terminate the growth, and cooling was performed at acooling rate of 25° C/min. At the time point where the substratetemperature became 600° C., the supply of NH₃ gas was stopped. Thesamples were cooled, taken out, and immersed in hydrochloric acid, sothat the scandium nitride film was selectively etched to separate theAlN template substrate for growth to obtain a GaN single crystalfree-standing substrate having a diameter of two inches and a thicknessof 163 μm.

Thus, the present invention has been explained in details givingspecific examples in embodiments and examples. However, the presentinvention is not limited to the above embodiments and examples of theinvention, and can be modified or varied without departing from thescope the present invention.

INDUSTRIAL APPLICABILITY

A Group III nitride semiconductor growth substrate of the presentinvention comprises a crystal growth substrate including a surfaceportion composed of a Group III nitride semiconductor which contains atleast Al, and a scandium nitride film formed on the surface portion.Thus, without greatly reducing the crystallinity of a Group III nitridesemiconductor layer Al_(x)Ga_(y)In_(1-x-y)N (0≦x≦1, 0≦y≦1, 0≦x+y≦1) tobe formed later, the Group III nitride semiconductor layer can be easilyseparated from the crystal growth substrate by chemical lift-off.

Further, in chemical lift-off; an acid solution is used as an etchant,which allows the Group III nitride semiconductor layer to be easilyseparated from the crystal growth substrate. As the etchant, ahydrochloric acid aqueous solution, a nitric acid aqueous solution, amixed acid of sulfuric acid and nitric acid, organic acid, or the likecan be used, and an acid solution which dissolves only ScN withoutdissolving the materials of the support substrate or the electrode to beused is appropriately selected.

Furthermore, according to the present invention, the above Group IIInitride semiconductor growth substrate is used, which allows thesubstrate to be removed by chemical lift-off. Besides, a Group IIInitride semiconductor epitaxial substrate, a Group III nitridesemiconductor element, and a Group III nitride semiconductorfree-standing substrate, which have good crystallinity can be provided,which can cover all wavelengths (200 nm to 1.5 μm) covered by a GroupIII nitride semiconductor material which exceeds the wavelength limit ofthe case of using a CrN material, in other words, which can cover thegrowth temperature range of the whole composition range ofAl_(x)Ga_(y)In_(1-x-y)N (0≦x≦1, 0≦y≦1, 0≦x+y≦1) including from AlN grownat a high temperature of 1200° C. or more to InN grown at a temperatureof about 500° C.

Moreover, according to the present invention, a step of forming a metallayer made of a Sc material on a crystal growth substrate a surfaceportion composed of a Group III nitride semiconductor which contains atleast Al, and a step of performing a nitriding process to the metallayer are provided. Thus, a Group III nitride semiconductor growthsubstrate can be produced such that the Group III nitride semiconductorlayer can be easily separated from the crystal growth substrate bychemical lift-off without greatly reducing the crystallinity of theGroup III nitride semiconductor layer Al_(x)Ga_(y)In_(1-x-y)N (0≦x≦1,0≦y≦1, 0≦x+y≦1) to be formed later.

In addition, in accordance with the present invention, chemical lift-offis performed using the above Group III nitride semiconductor growthsubstrate. Thus, a Group III nitride semiconductor epitaxial substrate,a Group III nitride semiconductor element, and a Group III nitridesemiconductor free-standing substrate, which have good crystallinity canbe produced efficiently, which can cover all wavelengths (200 nm to 1.5μm) covered by a Group III nitride semiconductor material which exceedsthe wavelength limit of the case of using a CrN material.

DESCRIPTION OF REFERENCE NUMERALS

-   1 Group III nitride semiconductor growth substrate-   2 surface portion-   3 crystal growth substrate-   4 scandium nitride film-   5 initial growth layer-   5 a first buffer layer-   5 b second buffer layer-   6 base substrate-   7 Group III nitride semiconductor layer-   8 Group III nitride semiconductor epitaxial substrate-   9 Group III nitride semiconductor element-   10 support substrate-   11 n-AlGaN layer-   12 AlInGaN-based quantum well active layer-   13 p-AlGaN layer

1. A method of producing a Group III nitride semiconductor growthsubstrate, comprising: a step of forming a metal layer made of a Scmaterial on a crystal growth substrate including a surface portioncomposed of a Group III nitride semiconductor which contains at leastAl, and a step of performing a nitriding process by heating the metallayer in an ambient gas containing an ammonia gas, thereby forming ascandium nitride film.
 2. The method of producing a Group III nitridesemiconductor growth substrate, according to claim 1, wherein theambient gas containing the ammonia gas is a mixed gas further containingone or more selected from an inert gas and a hydrogen gas.
 3. The methodof producing a Group III nitride semiconductor growth substrate,according to claim 1, wherein a highest temperature for heating themetal layer is in the range of 850° C. to 1300° C., and heating time at850° C. or higher is 1 min to 120 min.
 4. The method of producing aGroup III nitride semiconductor growth substrate, according to claim 1,further comprising a step of forming an initial growth layer composed ofat least one layer of a buffer layer made of Al_(x)Ga_(1-x)N (0≦x≦1) onthe scandium nitride film after the step of the nitriding process.
 5. Amethod of producing a Group III nitride semiconductor element,comprising: a step of forming a metal layer made of a Sc material on acrystal growth substrate including a surface portion composed of a GroupIII nitride semiconductor which contains at least Al; a step ofperforming a nitriding process by heating the metal layer in an ambientgas containing an ammonia gas to form a scandium nitride film, therebyproducing a Group III nitride semiconductor growth substrate; a step ofepitaxially growing at least one layer of a Group III nitridesemiconductor layer over the Group III nitride semiconductor growthsubstrate, thereby producing a Group III nitride semiconductor epitaxialsubstrate; a step of isolating the Group III nitride semiconductor layerinto a plurality of elements; a step of forming a support substrate onthe Group III nitride semiconductor layer side; and a step of separatingthe Group III nitride semiconductor layer from the crystal growthsubstrate by chemical lift-off by selectively etching the scandiumnitride film, thereby obtaining a Group III nitride semiconductorelement.
 6. The method of producing a Group III nitride semiconductorelement, according to claim 5, wherein the Group III nitridesemiconductor layer is grown at a highest temperature in the range of900° C. to 1300° C. in the step of producing the Group III nitridesemiconductor epitaxial substrate.
 7. The method of producing a GroupIII nitride semiconductor element, according to claim 5, furthercomprising a step of forming an initial growth layer composed of atleast one layer of a buffer layer made of Al_(x)Ga_(1-x)N (0≦x≦1) on thescandium nitride film after performing the nitriding process.
 8. Themethod of producing a Group III nitride semiconductor element, accordingto claim 7, wherein the initial growth layer is composed of a firstbuffer layer and a second buffer layer grown on the first buffer layer,a growth temperature of the first buffer layer is in the range of 900°C. to 1260° C., a growth temperature of the second buffer layer is inthe range of 1030° C. to 1300° C., and the growth temperature of thefirst buffer layer is equal to or lower than the growth temperature ofthe second buffer layer.
 9. A method of producing a Group III nitridesemiconductor free-standing substrate, comprising: a step of forming ametal layer made of a Sc material on a crystal growth substrateincluding a surface portion composed of a Group III nitridesemiconductor which contains at least Al; a step of performing anitriding process by heating the metal layer in an ambient gascontaining an ammonia gas to form a scandium nitride film, therebyproducing a Group III nitride semiconductor growth substrate; a step ofepitaxially growing at least one layer of a Group III nitridesemiconductor layer over the Group III nitride semiconductor growthsubstrate; and a step of separating the Group HI nitride semiconductorlayer from the crystal growth substrate by chemical lift-off byselectively etching the scandium nitride film, thereby obtaining a GroupIII nitride semiconductor free-standing substrate.
 10. The method ofproducing a Group III nitride semiconductor free-standing substrate,according to claim 9, wherein the Group III nitride semiconductor layeris grown at a highest temperature in the range of 900° C. to 1300° C. inthe step for producing the Group III nitride semiconductor epitaxialsubstrate.